Metallic microswimmers driven up the wall by gravity

Experiments on autophoretic bimetallic nanorods propelling within a fuel of hydrogen peroxide show that tail-heavy swimmers preferentially orient upwards and ascend along inclined planes. We show that such gravitaxis is strongly facilitated by interactions with solid boundaries, allowing even ultraheavy microswimmers to climb nearly vertical surfaces. Theory and simulations show that the buoyancy or gravitational torque that tends to align the rods is reinforced by a fore-aft drag asymmetry induced by hydrodynamic interactions with the wall.

Automated summary

This study demonstrates that tail-heavy swimmers have a preference for upward orientation and ascending along inclined planes when propelled by autophoretic bimetallic nanorods in hydrogen peroxide fuel. The interaction with solid boundaries greatly facilitates this gravitaxis, allowing even extremely heavy microswimmers to climb nearly vertical surfaces. The theory and simulations suggest that the alignment of the rods is reinforced by a fore-aft drag asymmetry induced by hydrodynamic interactions with the wall.